Distribution network power line communication system

Abstract

A distribution network power line communication system which includes coupling means for applying a carrier current communication signal to the polyphase primary distribution conductors with a proportional relationship between the signal voltages applied to the various conductors selected to provide a predetermined propagation mode. Impedance elements are connected between the conductors at selected points remote from the coupling point, such as at the location of unbalanced loads, line taps, branches, capacitor banks, distribution transformers, and other line discontinuities which may cause mode conversion. The impedance elements are selected and connected to re-establish the predetermined propagation mode.

We claim as our invention: 
     
       1. A polyphase, power frequency, distribution network power line carrier communication system, comprising: a plurality of distribution network power line conductors to which a carrier signal is to be coupled,   means providing a carrier signal having a frequency substantially higher than power frequency,   means coupling said carrier signal to each of said conductors to provide a predetermined proportional relationship between the carrier signals of said conductors,   and impedance elements connected between said conductors remote from the signal coupling point, said impedance elements being devoid of connection to said means providing the carrier signal, other than through said distribution network power line conductors, said impedance elements being selected to present a high impedance to power frequency and substantially lower impedances to the frequency of the carrier signal, said impedance elements also being selected to re-establish said predetermined proportional relationship between the carrier signals of said conductors.   
     
     
       2. The distribution network power line carrier communication system of claim 1 wherein the predetermined proportional relationship is a carrier signal voltage profile in which at least one of carrier signal voltages has a magnitude which differs from the magnitudes of the other carrier signal voltages. 
     
     
       3. The distribution network power line carrier communication system of claim 1 wherein the predetermined proportional relationship is a carrier signal voltage profile in which the magnitudes of all of the carrier signal voltages are different. 
     
     
       4. The distribution network power line carrier communication system of claim 1 wherein the predetermined proportional relationship is a carrier signal voltage profile in which the magnitudes of all of the carrier signal voltages are substantially the same. 
     
     
       5. The distribution network power line carrier communication system of claim 1 wherein the plurality of distribution network power line conductors to which the carrier signal is coupled are the phase conductors. 
     
     
       6. The distribution network power line carrier communication system of claim 1 wherein the plurality of conductors to which the carrier signal is coupled are the phase and neutral conductors. 
     
     
       7. The distribution network power line carrier communication system of claim 1 wherein the means providing the carrier signal includes transmitter means, and the means coupling the carrier signal to the conductors includes a transformer having a primary winding connected to said transmitter means, and a secondary winding connected to the conductors. 
     
     
       8. The distribution network power line carrier communication system of claim 7 wherein the secondary winding has taps thereon, and including a plurality of capacitors, with certain of the taps being connected to predetermined conductors via said capacitors. 
     
     
       9. The distribution network power line carrier communication system of claim 7 wherein the secondary winding has taps thereon, and including a plurality of capacitors, with at least one of the taps being connected to different conductors via different capacitors. 
     
     
       10. The distribution network power line carrier communication system of claim 7 including a plurality of capacitors, and wherein each conductor is connected to a common point on the secondary winding of the transformer via a different one of said plurality of capacitors. 
     
     
       11. The distribution network power line carrier communication system of claim 1 wherein the means providing the carrier signal includes transmitter means, and the means coupling the carrier signal to the conductors includes an autotransformer connected to said transmitter means and to the conductors. 
     
     
       12. The distribution network power line carrier communication system of claim 11 including a plurality of capacitors, and wherein each conductor is connected to a common point on the autotransformer via a different one of said plurality of capacitors. 
     
     
       13. The distribution network power line carrier communication system of claim 11 wherein the autotransformer has taps thereon, and including a plurality of capacitors, with certain of the taps being connected to predetermined conductors via said capacitors. 
     
     
       14. The distribution network power line carrier communication system of claim 11 wherein the autotransformer has taps thereon, and including a plurality of capacitors, with at least one of the taps being connected to different conductors via different capacitors. 
     
     
       15. The distribution network power line carrier communication system of claim 1 wherein the means coupling the carrier signal to the conductors includes a first transformer having taps, and a first plurality of capacitors connected from predetermined taps to the conductors, and wherein the impedance elements connected to the conductors include a second transformer, similar to the first, and a second plurality of capacitors similar to the first plurality, connected from predetermined taps of the second transformer to the conductors in a manner similar to the connection of the first plurality of capacitors to the conductors. 
     
     
       16. The distribution network power line carrier communication system of claim 1 wherein the means coupling the carrier signal to the conductors includes a transformer and a plurality of capacitors which couples the carrier signal substantially equally to each of the conductors, and the impedance elements are selected to force the carrier signals to be substantially equal to one another. 
     
     
       17. The distribution network power line carrier communication system of claim 16 wherein the impedance elements are capacitors. 
     
     
       18. The distribution network power line carrier communication system of claim 16 wherein the impedance elements are series capacitance-inductance circuits tuned to resonance at the frequency of the carrier signal.